Fuel cells are devices that directly convert chemical energy of fuel cells into electrical energy. Fuel cells based on polymer electrolyte (PEFC) have been extensively studied for their potential applications in transportation, stationary, and portable energy devices, see N. C. Otto, P. F. Howard, Fuel Cell Seminar-Program and Abstracts, Orlando, Fla., pp. 559-562, Nov. 17-20, 1996, the disclosure of which is incorporated herein by reference. Three types of PEFC can be visualized based on the nature of the fuel used in these systems. These are: 1) H2/Air fuel cells, which use pristine hydrogen, 2) Reformate/Air fuel cell, which uses hydrogen generated by reforming fossil fuels such as methanol and gasoline, and 3) Direct Methanol fuel cell, where methanol is used as a fuel and is directly oxidized at the anode.
In the H2/Air fuel cell, the hydrogen electrode generally performs satisfactorily with an overpotential of about 20-30 mV at the operating current densities of 200-400 mA/cm2. In reformate fuel cells, however, their performance is greatly diminished due to carbon monoxide and sulfur poisoning. These impurities are always present in the hydrogen stream produced during reforming of natural gas or petroleum. Typically, the water gas shift reaction used in the reformate fuel cells reduces the CO content to only about 1%. This is relatively higher than the CO tolerance of a typical anode catalyst. The CO poisoning is the most critical problem in the solid electrolyte fuel cells operating at 100° C., because even very small CO levels can be detrimental to the performance of the hydrogen electrode, see H. P. Dhar, L. G. Christner, A. K. Kush, J. Electrchem. Soc., 134, 3021 (1987), the disclosure of which is incorporated herein by reference. The CO poisoning results in overall voltage losses for the fuel cell due to high anodic polarization. It has been shown that the presence of even 30 ppm carbon monoxide in the reformate gas significantly reduces the performance of 5 kW Ballard fuel cell, see S. Swathirajan, 1994 Fuel Cell Seminar, Ext. Abs., 204 (1994), the disclosure of which is incorporated herein by reference. Several solutions have been proposed to alleviate the CO poisoning problem. These solutions include water-gas shift reaction, membrane separation (Pd—Ag membrane) process, and introducing oxygen into hydrogen-CO containing fuels.
For DMFC, on the other hand, sluggish kinetics of methanol oxidation and methanol cross-over are the main barriers for its commercialization. The sluggish kinetics of the methanol electrooxidation is due to the poor catalytic activity of platinum anodes for the anode reaction:CH3OH+H2O→CO2+6H++6e−
On a clean pristine platinum surface, the methanol electrooxidation is quite rapid. However, the formation of carbon monoxide as an intermediate in the above reaction poisons the platinum surface and hence greatly inhibits its activity toward methanol oxidation, see R. Parsons and T. VanderNoot, J. Electroanal. Chem., 9, 257 (1988).
In recent years, a new class of materials has been developed by dispersing layered silicates with polymers at the nanoscale level. These new materials have attracted wide interest because they often exhibit chemical and physical characteristics that are very different from the starting materials, see K. A. Carrado. Appl. Clay Sci. 17, 1, 2000, K. A. Carrado, in Advanced Polymeric Materials: Structure Property Relationships, S. G. Advani, G. O. Shonaike, Eds.; CRC Press LLC, Boca Raton, Fla., 2003, pp. 349-396, and G. Sandi, H. Joachin, R. Kizilel, S. Seifert, and K. A. Carrado, Chemistry of Materials, 15 (4), 838, 2003, the disclosures of which are incorporated herein by reference. In some cases, the silicates and polymers exist as alternating layers of inorganic and organic, see K. A. Carrado, L. Xu, S. Seifert, R. Csencsits, C. A. Bloomquist, in Polymer-Clay Nanocomposites, G. Beall & T. J. Pinnavaia, Eds., Wiley & Sons: UK, 2000, pp. 47-63 and G. Sandi, K. A. Carrado, H. Joachin, W. Lu and J. Prakash, Journal of Power Sources, 119-121, 492, 2003, the disclosures of which are incorporated herein by reference. Nanocomposite materials of PEO and phyllosilicates were first suggested by Ruiz-Hitzky and Aranda, see E. Ruiz-Hitzky, P. Aranda, Adv. Mater, 2, 545, 2003, incorporated herein by reference, as candidates for polymer electrolytes. Within these materials, the polymer chains are intercalated between the silicate layers. The polymer chains then provide a mobile matrix in which cations are able to move. A considerable amount of interest has been shown in nanocomposites of PEO and montmorillonite, a layered aluminosilicate clay. When this composite contains LiBF4, it displays conductivities up to 2 orders of magnitude larger than that of PEO itself at ambient temperatures. However, the addition of lithium salts, which is needed to obtain such conductivity values, is not desirable for two reasons; the first relates to a more complicated synthetic route and the second is that transference numbers are not unity since in this case both cations and anions move.